The Study of Fault Valve Behaviour by Using Microearthquake Source Parameters

Abstract:

The main purpose of this research is to study the fault-valve behaviour by using a nonlinear waveform inversion to investigate the microearthquake source parameters around the fault-valve area. We have built up an efficient procedure which incorporates with parallel computing to accomplish the above goal. We adopted the nonlinear search algorithm (Neighborhood Algorithm, NA) to explore the parameter space and construct a source model to calculate the theoretical waveform simulation by adopting the three dimensional numerical calculation. By minimizing the misfit between synthetic and observed seismograms, through the nonlinear search algorithm, we are able to obtain more precise fault plane solutions by using the less station distribution. Combining all these methods with parallel computer clusters, it allows us to perform the waveform inversion with less time consuming. Therefore, we applied the above procedures to investigate the microearthquakes that occurred in the Chukou fault, which is the main collision front in the West Foothills, Taiwan. Our results indicate that the highly agreement between the observed and the synthetic waveforms suggest the reliability of the focal mechanism. The results are not only giving better understanding the seismogenic structure beneath the West Foothills in Taiwan , but also can allow us to identify waveform characteristics caused by the source heterogeneity or fluid effect. Due to the valve action on the fault plane may exhibit variation in fault strength, the large fluid pressure around the valve area would also take effect to the microearthquakes. Thus, the derived source parameters obtained from this study can serve as a detail physical status to investigate the seismongenic structures beneath the fault zone for future research.